A solid electrolytic capacitor encapsulated with a resin is manufactured by a method which one or not less than two solid electrolytic capacitor elements are arranged on a lead frame and then the solid electrolytic capacitor elements are dipped in the resin solution, a method which transfer molding is carried out using a melted resin, or the like. The dipping method in the resin solution provides a thin resin capsula, which is likely to cause a pinhole and low dimensional accuracy. On the other hand, the transfer molding method, in comparison to the dipping method, gives a molded product having fleshier and complex shape, with uniform quality, and high dimensional accuracy, short hardening time, and fewer burrs, and post handling is easier. Therefore, the transfer molding method is adopted in many cases of manufacturing a large amount of solid electrolytic capacitors.
However, pressure and calories applied to the solid electrolytic capacitors from a melted resin are high in the transfer molding method. Therefore, in encapsulation with the resin by the transfer molding method, deterioration of the solid electrolytic capacitor element might occur and then ESR might rise. Solid electrolytic capacitors with small value of ESR are used in recent years. A little rise of ESR cannot be overlooked in a design of an electronics device.
As a method of reducing level of ESR, for example, patent document 1 discloses a method for manufacturing a solid electrolytic capacitor anode body, wherein the method comprises the steps of: mixing a valve action metal powder, a solid water soluble binder and an organic solvent soluble binder in an organic solvent, granulating the mixture; forming a molded article so as to plant an anode lead on the granulated object; washing the molded article with a solvent to remove the binder in the molded article, and sintering the molded article in high temperature and vacuum. In patent document 1, it is described that using this anode body provides a solid electrolytic capacitor having a small level and variation in tan δ and ESR and being improved in a leakage current characteristic.
Patent document 2 discloses a method for manufacturing a solid electrolytic capacitor, wherein the method comprises the steps of: winding an anode foil and a cathode foil through a separator to prepare a winding element; immersing the winding element in a solvent capable of dissolving at least one component of the separator to decrease the weight of the separator; and then forming a solid electrolyte layer in the winding element.
Patent document 3 discloses a method for manufacturing a solid electrolytic capacitor, wherein the method comprises the steps of winding a anode foil having oxide layers on their surfaces and a cathode foil through a separator to obtain a capacitor element, sequentially dipping the capacitor element in an oxidizing reagent solution and a polymerizable monomer solution, and then chemically polymerizing the polymerizable monomer to form an electrically-conductive polymer layer in a capacitor element, in which the solvent of the polymerizable monomer solution is an ionic liquid, the ionic liquid in the capacitor element is dissolved and removed by immersing the capacitor element in a solvent capable of dissolving the ionic liquid after the forming step of the electrically-conductive polymer. In patent document 3, it is described that this manufacture method can provide a solid electrolytic capacitor having a high appearance ratio of an electrostatic capacitance, a high electric capacitance, and a low leakage current.
Patent document 4 discloses a method for manufacturing a solid electrolytic capacitor, wherein the method comprises the steps of: setting up a layer of silicone resin or a silicone oil on a solid electrolytic capacitor element comprising an anode body, a dielectric layer, a carbon graphite layer and a silver paste layer, immersing the element in an organic solvent such as acetone and toluene or optionally with vibration to remove the silicone layer on the surface, then setting up a encapsulating resin layer. In patent document 4, it is described that this manufacture method can improve a moisture resistance of the solid electrolytic capacitor, resulting in reducing deterioration in an electrostatic capacity change ratio and a dielectric tangent.